Using the Accumeasure 9000 Capacitance Transducer Amplifier to Measure Position and Vibration Displacement of Small Targets - MTI Instruments - #1

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MTI Instruments, Inc. 325 Washington Avenue Extension Albany, NY 12205 PH: +1-518-218-2550 OR USA TOLL FREE: 1-800-342-2203 FX: +1-518-218-2506 sales@mtiinstruments.com www.mtiinstruments.com APPLICATION NOTE Using the Accumeasure 9000 Capacitance Transducer Amplifi er to Measure Position and Vibration Displacement of Small Targets Introduction Advances in nearly all fi elds of science, technology, and manufacturing has brought with it the need to measure the position and/or vibration displacement of very small mechanical parts and assemblies. The Problem Since these devices often operate at high speed and with relatively small movements, it usually dictates the use of noncontact sensors to insure that the natural movements are not compromised by the sensor itself as may happen when using contacting sensors. In addition, the noncontact sensor must be very small and have an even smaller spatial sensing capability. One such recent application required measurement of the position and vibration displacement amplitude of taut wires .002” to .005” (50 to 125 microns) in diameter. The Solution After several unsuccessful attempts at making this measurement using a variety of conventional noncontact sensors employing magnetics, optical, and capacitance technology, the customer turned to MTI Instruments for a solution to the problem. Fortunately, MTI Instruments had recently completed the development and market introduction of the AccumeasureT 9000 Capacitance Transducer Amplifi er, which can operate with up to 100X smaller capacitance sensing area than most previous capacitance sensors, while still maintaining acceptable levels of standoff distance and sensing range. This permitted MTI Instruments engineers to design a capacitance sensor with a sensing electrode only .005” wide x .050” long, which when operated with the Accumeasure 9000 amplifi er at full sensitivity could give a sensing range of up to .008”, as required by the application. The .005” wide dimension of the sensing element is aligned with the .003” diameter of the wire target and the .050” length dimension of the sensing element is aligned with the axial length of the wire target. Most previous capacitance transducer amplifi ers could only give about .0005” (500 micro inches) range with this size sensor, which would be far short of the customer’s requirement. MTII appnote: accumeasuresmall.pdf - Page 1 of 2